I do not prewash and do not starch fabrics for piecing (except a little spray starch once in awhile if I feel I need it for a block).
I do heavily starch the backing fabric and also the binding fabric before cutting the binding strips. For this I paint on a 1:1 solution of Sta-Flo liquid laundry starch and water, using a large wall painting brush, until the fabric is saturated. I toss in the dryer and then iron with steam. This helps prevent puckers when machine quilting and also keeps the binding nice and even.
I use Synthrapol in the first wash just in case there is any loose dye in the fabrics (and also to get rid of the starch).
Oh, and I do pretest any suspicious fabrics for bleeding before incorporating them into a quilt. For this I just toss a small piece in a glass of water, look for bleeding, and also rub the damp piece against white fabric to make sure there is no dye transfer. For pastel fabrics, I wouldn't bother to pretest.